The present invention relates to exhaust gas recirculation valves and, more particularly, to a modular metering subassembly having a gas arrestor.
Exhaust gas recirculation (EGR) valves capture engine exhaust and recycle at least a portion of that captured exhaust gas into the combustion chamber of the engine to improve combustion. Exhaust gas is used since it is readily available and contains only a small amount of oxygen. Adding the exhaust gas to the air in the combustion chamber has the effect of lowering the combustion temperature below the point at which nitrogen combines with oxygen. Thus, exhaust gas recirculation increases fuel economy and reduces the level of undesirable emissions.
Conventional EGR valves include an actuator and a metering base. The metering base includes a metering chamber having a metering port. The metering chamber has an end that is associated with the intake manifold or intake vacuum of the engine. The metering port is connected to a source of exhaust gas and provides a passageway for the flow of exhaust gas into the metering chamber. An elongate shaft extends contiguously in a longitudinal direction from the actuator, through an orifice in the metering base, into the metering chamber, and to the metering port. A metering poppet, which is a plunger-shaped member, is disposed at the end of the shaft proximate to the metering port. In a default position, the metering poppet abuttingly engages or is disposed within the metering port, thereby sealing the metering port. In this default position, no exhaust gas enters the metering chamber through the metering port. The shaft is reciprocated to displace the metering poppet from engagement with the metering port thereby unsealing the metering port and allowing exhaust gas to flow through the metering port into the metering chamber and into the intake manifold of the engine. Thus, the reciprocal motion of the shaft and metering poppet selectively control the flow of exhaust gas into the intake air stream of the engine.
The contiguous shaft extends from within the actuator and terminates proximate the metering port. In order for the EGR valve to operate properly, the shaft must pass in a substantially concentric manner through the actuator orifice, through the orifice in the metering assembly, and into the metering port. Typically, due to manufacturing tolerances and process variation, these orifices are not perfectly concentric. As the shaft is reciprocated within these non-concentric orifices, the shaft may rub or perhaps even bind against one of the orifices. Furthermore, the metering poppet may rub or otherwise interfere with the metering port. Thus, increased frictional forces may be encountered during reciprocation of the shaft. Similarly, if the shaft as installed is not substantially perpendicular to the orifices, increased frictional forces may also be encountered during reciprocation of the shaft. In order to reciprocate the shaft these frictional forces must be overcome. Therefore, the actuator must provide a substantially larger force in order to overcome the increased friction and reciprocate the shaft. An actuator which is capable of overcoming the frictional forces typically must be larger in size and greater in weight than would be necessary if those frictional forces were minimized or eliminated.
Space is at a premium within the cramped engine compartments of the technologically-advanced vehicles of today. Furthermore, automobile manufactures are continuously striving to reduce the weight of vehicles to thereby improve fuel economy. These design considerations dictate that EGR valves, and the components thereof, be as compact and as light as possible. Therefore, it is desirable to make actuators as small and as light as is practicable. However, the actuator must be capable of producing enough power to overcome the frictional forces. The presence of these frictional forces place a limit upon the reductions in actuator size and weight which are obtainable in practice.
Conventional EGR valves do not sufficiently seal the actuator from the metering chamber and the exhaust gases carried thereby. More particularly, conventional EGR valves typically employ a journal bearing disposed around the actuator shaft. Some clearance must exist between the journal bearing and the shaft in order for the shaft to be freely reciprocated by the actuator. Thus, the journal bearing does not completely seal exhaust gases from penetrating into the actuator through the clearance between the journal bearing and the shaft. This makes possible the convection of exhaust gases into the actuator. Furthermore, fluctuating pressures and high back pressure in the exhaust and intake manifolds tend to force the exhaust gas through the clearance between the journal bearing and the shaft, and into the actuator. Exhaust gas typically has a high moisture content and is also highly corrosive. The intrusion of exhaust gas into the actuator can result in malfunction or even premature failure of the actuator.
Therefore, what is needed in the art is an EGR valve which reduces the need for concentricity of the shaft relative to the actuator orifice, the metering orifice, and the metering port.
Furthermore, what is needed in the art is an EGR valve which has a reduced sensitivity to manufacturing tolerances and process variations in the shaft, and in the alignment of the shaft relative to the actuator orifice, the metering orifice, and the metering port.
Moreover, what is needed in the art is an EGR valve which reduces the intrusion of exhaust gas into the actuator.
The present invention provides a metering subassembly having a gas arrester for use in a modular EGR valve.
The present invention comprises, in one form thereof, a metering subassembly having an elongate metering shaft. A flanged end of the metering shaft is disposed a predetermined distance above a top surface of the metering subassembly. The metering subassembly is configured for being coupled to an actuator subassembly such that the flanged end of the metering shaft is disposed proximate the actuator subassembly. A gas arrestor includes a side wall interconnected with a collar. The collar surrounds a periphery of the flanged end. The side wall extends from the collar in a direction generally toward the top surface of the metering subassembly.
An advantage of the present invention is that the adverse effects of a shaft being non-concentric relative to the actuator orifice is reduced.
Another advantage of the present invention is that sensitivity to manufacturing tolerances and process variation in the alignment of the actuator and the metering base to is reduced.
An even further advantage of the present invention is that it reduces the penetration of exhaust gas into the actuator.